Views: 277 Author: Site Editor Publish Time: 2021-05-27 Origin: Site
In the open system, the hydraulic pump 1 sucks oil from the oil tank 5, supplies oil to the hydraulic cylinder 3 through the reversing valve 2, and the return oil of the hydraulic cylinder 3 returns to the oil tank through the reversing valve. As the finished oil is returned to the tank, it can play the role of heat dissipation and precipitation of impurities. However, as the oil is often in contact with air, the air is easy to infiltrate into the system, leading to the need to set the counterbalance valve on the road, which will cause additional energy loss, making the oil temperature rise. Because of the simple structure of the open system, it is still used by most cranes.
(1) Generally, we use double pump or three pump oil supply, pilot oil is supplied by a separate pilot pump. If the power required by the hydraulic actuator is very big, we need to merge oil supply. There are two ways of confluence: (1) Inside valve confluence. In general, the double pump confluent supply to a valve stem, and then the valve stem provides the required oil for hydraulic actuators. (2) outside valve confluence. The two pumps feed oil to the required hydraulic actuators through their respective stem and merge outside the stem.
(2) Multiplex valves are usually used for oil supply in blocks and pump separately. Each valve group can use straight oil supply channel or parallel oil supply channel according to actual needs. The former can achieve priority oil supply, the latter can achieve combined oil supply.
(3) Another disadvantage of the open circuit is that when a pump is used by more than one actuator, the hydraulic oil first flows to the lightly loaded actuator, making it difficult for the high-loaded actuator to operate. Therefore, the control stem of the lightly loaded actuator needs to be throttled.
In a closed system, the inlet pipe of the hydraulic pump is directly connected with the return pipe of the actuator, and the working liquid is closed in the pipeline of the system. The structure a closed system is relatively compact. Besides, because of less contact with air, the stability of this system is good. The variable speed and reversing mechanism of the working mechanism is realized by adjusting the variable mechanism of the pump or motor, which avoids the hydraulic impact and energy loss in the process of reversing in the open system.
The closed system is more complicated than the open system. Because the oil in the closed system does not return to the tank after it finished its work, the heat dissipation and filtration conditions of the oil are worse than that of the open system. In order to make up for this shortcoming, we usually add a small capacity of rehydration pump for oil and heat dissipation, so this kind of system is actually a semi-closed system.
（1) current variable pumps in a closed system all have integrated structures, in which oil pump, oil tonic, overflow and control valve group are all on the hydraulic pump, so the pipeline connection becomes simple. Not only it reduces the installation space, but also reduce the leakage and piping vibration caused by pipeline connection.
（2) Since only a small amount of oil is drawn from the tank, loss of the tank can be reduced greatly.
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